CBSE Class 12th Physics Dual Nature of Radiation and Matter 100 MCQs

Physics – Dual Nature of Radiation and Matter

Class 12 Physics (Chapter 11) • 100 Multiple Choice Questions

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Question 1

What is the rest mass of a photon?

Correct Answer: Zero

Question 2

The energy of a photon of frequency ν and wavelength λ is given by:

Correct Answer: E = hν = h c / λ

Question 3

What is the momentum of a photon of frequency ν?

Correct Answer: p = hν / c = h / λ

Question 4

Work function (Φ₀) of a metal is defined as:

Correct Answer: Minimum energy required to eject an electron from the metal surface

Question 5

Threshold frequency (ν₀) is the:

Correct Answer: Minimum frequency of incident light required for photoelectric emission

Question 6

Einstein's photoelectric equation is expressed as:

Correct Answer: K_max = hν - Φ₀ = e V_s

Question 7

Stopping potential (V_s) is the minimum negative potential given to the anode that makes photoelectric current:

Correct Answer: Zero

Question 8

De Broglie wavelength (λ) associated with a particle of mass m and momentum p is given by:

Correct Answer: λ = h / p = h / (m v)

Question 9

De Broglie wavelength of an electron accelerated through a potential difference V is given approximately by:

Correct Answer: λ = 1.227 / √V nm

Question 10

Davisson-Germer experiment demonstrated:

Correct Answer: Wave nature of electrons (electron diffraction)

Question 11

Photoelectric current is directly proportional to:

Correct Answer: Intensity of incident radiation

Question 12

Maximum kinetic energy of photoelectrons depends upon:

Correct Answer: Frequency of incident light

Question 13

Who discovered the photoelectric effect experimentally?

Correct Answer: Heinrich Hertz

Question 14

Who successfully explained the photoelectric effect using the quantum theory of light (photons)?

Correct Answer: Albert Einstein

Question 15

What is the value of Planck's constant (h)?

Correct Answer: 6.626 × 10⁻³⁴ J·s

Question 16

The photoelectric emission is an instantaneous process meaning time lag between incidence and emission is roughly:

Correct Answer: Less than 10⁻⁹ seconds (virtually zero)

Question 17

Which of the following graphs between stopping potential (V_s) and frequency (ν) of incident light is a straight line?

Correct Answer: Straight line with slope equal to h/e

Question 18

What is the de Broglie wavelength of a neutron of mass m at absolute temperature T? (k is Boltzmann constant)

Correct Answer: λ = h / √(3 m k T)

Question 19

If the momentum of a particle is doubled, its de Broglie wavelength becomes:

Correct Answer: Halved

Question 20

Which of the following particles has the longest de Broglie wavelength for the same velocity?

Correct Answer: Electron (due to smallest mass)

Question 21

What is the dimensional formula of Planck's constant (h)?

Correct Answer: [M L² T⁻¹]

Question 22

Which of the following physical quantities has the same dimensions as angular momentum?

Correct Answer: Planck's constant (h)

Question 23

Threshold wavelength (λ₀) and threshold frequency (ν₀) are related as:

Correct Answer: λ₀ = c / ν₀

Question 24

Photoelectric emission is possible only if the incident light has frequency:

Correct Answer: Greater than or equal to threshold frequency (ν ≥ ν₀)

Question 25

What is the effect of increasing the intensity of incident light on stopping potential?

Correct Answer: Stopping potential remains unchanged (constant)

Question 26

What is the effect of increasing the frequency of incident light on stopping potential?

Correct Answer: Stopping potential increases linearly

Question 27

Who suggested the concept of matter waves (wave-particle duality for matter)?

Correct Answer: Louis de Broglie

Question 28

Why are wave properties not observable for macroscopic objects (like a moving car or cricket ball)?

Correct Answer: Because their mass is so large that de Broglie wavelength is extremely small (undetectable)

Question 29

What is the de Broglie wavelength of an alpha particle accelerated through potential V compared to an electron?

Correct Answer: Shorter (due to larger mass and charge of alpha particle)

Question 30

What is the momentum of a photon of wavelength 500 nm?

Correct Answer: 1.33 × 10⁻²⁷ kg·m/s

Question 31

What is the threshold frequency for a metal whose work function is 2 eV?

Correct Answer: 4.83 × 10¹⁴ Hz

Question 32

In Davisson-Germer experiment, electron beam was accelerated using a nickel target and scattered electrons were observed at various:

Correct Answer: Scattering angles

Question 33

What was the prominent scattering angle at which a sharp peak in electron intensity was observed in Davisson-Germer experiment?

Correct Answer: 50° (at accelerating voltage 54V)

Question 34

Which of the following phenomena cannot be explained by wave theory of light but is explained by photon theory?

Correct Answer: Photoelectric effect

Question 35

What is the de Broglie wavelength of an electron accelerated through 100 V?

Correct Answer: 0.123 nm (or 1.23 Å)

Question 36

What is the relation between kinetic energy K and momentum p of a particle of mass m?

Correct Answer: K = p² / (2m)

Question 37

Express de Broglie wavelength in terms of kinetic energy K and mass m:

Correct Answer: λ = h / √(2 m K)

Question 38

What happens to the photoelectric current if the distance between the light source and the cathode is increased?

Correct Answer: Decreases (due to decrease in intensity)

Question 39

Which of the following metals is most suitable for photoelectric emission using visible light due to very low work function?

Correct Answer: Cesium / Potassium (Alkali metals)

Question 40

What is the unit of work function?

Correct Answer: Electron-volt (eV) or Joule (J)

Question 41

Who received the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect?

Correct Answer: Albert Einstein

Question 42

Who received the Nobel Prize in Physics in 1929 for discovering the wave nature of electrons?

Correct Answer: Louis de Broglie

Question 43

What happens to the stopping potential if the frequency of incident radiation is increased while keeping intensity constant?

Correct Answer: Increases

Question 44

What happens to the photoelectric saturation current if the intensity of incident radiation of suitable frequency is increased?

Correct Answer: Increases proportionally

Question 45

Which of the following describes the particulate nature of light?

Correct Answer: Light travels in discrete packets of energy called photons

Question 46

What is the de Broglie wavelength of an electron with kinetic energy of 1 eV?

Correct Answer: 1.227 nm (12.27 Å)

Question 47

The concept that light has both wave and particle aspects is known as:

Correct Answer: Wave-particle duality

Question 48

Which of the following statements about photons is correct?

Correct Answer: Photons are electrically neutral and are not deflected by electric or magnetic fields

Question 49

In a photoelectric experiment, if the potential difference between cathode and anode is made positive and increased, the photocurrent:

Correct Answer: Increases initially and then reaches a saturation value

Question 50

What is the de Broglie wavelength associated with an electron of kinetic energy K when expressed in terms of V (accelerating voltage)?

Correct Answer: λ = h / √(2 m e V)

Question 51

What is the slope of the Einstein's stopping potential (V_s) versus frequency (ν) curve?

Correct Answer: h / e

Question 52

Does the maximum kinetic energy of photoelectrons depend on the intensity of incident light?

Correct Answer: No, it is independent of intensity

Question 53

In a photoelectric setup, if the frequency of light is doubled while remaining above threshold frequency, what happens to maximum kinetic energy?

Correct Answer: More than doubles (K_max' = 2hν - Φ₀ > 2K_max)

Question 54

What is the de Broglie wavelength of a photon of energy E?

Correct Answer: λ = h c / E

Question 55

Which experiment confirmed the particulate nature of radiation through momentum transfer (photon collision with electrons)?

Correct Answer: Compton scattering

Question 56

What is the frequency of a photon whose energy is 1 eV?

Correct Answer: 2.42 × 10¹⁴ Hz

Question 57

In a photoelectric cell, light energy is converted directly into:

Correct Answer: Electrical energy (electric current)

Question 58

What is the de Broglie wavelength of a proton and an electron having the exact same kinetic energy?

Correct Answer: Electron has a longer wavelength (due to smaller mass)

Question 59

What is the de Broglie wavelength of a proton and an electron having the exact same momentum?

Correct Answer: Both have exactly equal de Broglie wavelengths (λ = h/p)

Question 60

Why does classical wave theory fail to explain photoelectric emission successfully?

Correct Answer: It predicts that time lag should occur at low intensities and kinetic energy should depend on intensity, neither of which happens

Question 61

What is the maximum velocity of photoelectrons emitted when light of frequency ν falls on a metal of work function Φ₀?

Correct Answer: v_max = √[2 (hν - Φ₀) / m]

Question 62

Which of the following describes the dual nature of matter?

Correct Answer: Particles like electrons and protons can exhibit wave properties under appropriate conditions

Question 63

What is the de Broglie wavelength of a thermal neutron at room temperature?

Correct Answer: Around 0.1 nm (comparable to interatomic spacing in crystals)

Question 64

If the accelerating potential in an electron microscope is increased, what happens to the resolving power of the microscope?

Correct Answer: Increases (because de Broglie wavelength decreases with higher voltage)

Question 65

What is the unit of momentum p in SI units?

Correct Answer: kg·m/s (or N·s)

Question 66

What is the momentum of a photon of wavelength λ in terms of Planck's constant?

Correct Answer: h / λ

Question 67

Which of the following statements about threshold frequency is true?

Correct Answer: It depends on the nature of the metal surface

Question 68

Why can ultraviolet light cause photoemission from a zinc plate while visible light cannot?

Correct Answer: Frequency of UV light is greater than the threshold frequency of zinc, whereas visible light frequency is lower

Question 69

What is the maximum kinetic energy of photoelectrons if stopping potential is 2.5 V?

Correct Answer: 2.5 eV (or 4.0 × 10⁻¹⁹ J)

Question 70

Which of the following particles does not exhibit de Broglie wave nature in principle?

Correct Answer: All particles (every moving particle has a de Broglie wavelength)

Question 71

What is the energy of a photon of wavelength 1000 Å in eV?

Correct Answer: 12.4 eV

Question 72

In a photoelectric experiment, the stopping potential is found to be 3V. What is the maximum kinetic energy of emitted electrons?

Correct Answer: 3 eV

Question 73

What is the de Broglie wavelength of an electron moving with 1% of the speed of light?

Correct Answer: 2.43 × 10⁻¹¹ m (0.243 Å)

Question 74

Which property of light is established by interference and diffraction?

Correct Answer: Wave nature

Question 75

Which property of light is established by the photoelectric effect?

Correct Answer: Particle nature (quantum nature)

Question 76

What is the momentum of a photon having energy 3 eV?

Correct Answer: 1.6 × 10⁻²⁷ kg·m/s

Question 77

What is the threshold wavelength for a metal with work function 3.1 eV?

Correct Answer: 4000 Å (400 nm)

Question 78

If the intensity of light in a photoelectric cell is doubled, what happens to the maximum speed of emitted photoelectrons?

Correct Answer: Remains unchanged

Question 79

What is the de Broglie wavelength of a stationary particle of finite mass?

Correct Answer: Infinite (since velocity and momentum are zero)

Question 80

Which of the following has the shortest de Broglie wavelength when moving with the same speed?

Correct Answer: Alpha particle (heaviest among options)

Question 81

What is the dimensional formula of momentum (p)?

Correct Answer: [M L T⁻¹]

Question 82

What is the threshold wavelength for potassium if its work function is 2.2 eV?

Correct Answer: 5640 Å (564 nm)

Question 83

In a photoelectric experiment, the graph of stopping potential versus frequency for different metals has:

Correct Answer: Same slope but different x-intercepts (threshold frequencies)

Question 84

What is the energy of a photon corresponding to ultraviolet light of wavelength 200 nm?

Correct Answer: 6.2 eV

Question 85

What is the de Broglie wavelength of a particle of mass m moving with speed c (speed of light)?

Correct Answer: λ = h / (m c)

Question 86

Which of the following conclusions was drawn from Davisson-Germer experiment?

Correct Answer: Confirmation of de Broglie hypothesis of matter waves

Question 87

What is the value of stopping potential if work function is 2 eV and incident photon energy is 5 eV?

Correct Answer: 3 V

Question 88

In a photoelectric cell, the current depends on intensity while stopping potential depends on:

Correct Answer: Frequency of incident radiation

Question 89

What is the de Broglie wavelength of an electron accelerated through a potential difference of 25 V?

Correct Answer: 0.245 nm (or 2.45 Å)

Question 90

Which of the following correctly describes the nature of light?

Correct Answer: It exhibits both wave and particle characteristics depending on the experiment

Question 91

What is the frequency of a photon with wavelength equal to 1 meter?

Correct Answer: 3.0 × 10⁸ Hz

Question 92

What is the energy of a photon of wavelength 600 nm in Joules?

Correct Answer: 3.31 × 10⁻¹⁹ J

Question 93

According to de Broglie, what is the wavelength of a particle of mass m moving with speed v?

Correct Answer: λ = h / (m v)

Question 94

What is the de Broglie wavelength of an electron if its kinetic energy is quadrupled (multiplied by 4)?

Correct Answer: Halved (becomes λ / 2)

Question 95

Which of the following experimental findings established the quantum nature of light energy transfer?

Correct Answer: Photoelectric effect threshold frequency and instant emission

Question 96

What is the de Broglie wavelength of a particle of mass m falling freely from rest through height h under gravity?

Correct Answer: λ = h / √(2 m² g h)

Question 97

What is the momentum of a photon whose wavelength is equal to the Compton wavelength (h / mc)?

Correct Answer: m c

Question 98

Which law states that energy and momentum are conserved in every individual photon-electron collision?

Correct Answer: Principle of conservation of energy and momentum (quantum mechanics)

Question 99

What is the de Broglie wavelength of an electron when its kinetic energy is equal to its rest mass energy? (Relativistic considerations)

Correct Answer: Shorter than the non-relativistic de Broglie wavelength formula prediction

Question 100

Why does a beam of electrons show diffraction patterns similar to X-rays when passed through a crystal?

Correct Answer: Due to the wave nature of electrons (de Broglie wavelength comparable to crystal spacing)